STEERING AXIS INCLINATION (S. A. I.)
Steering axis inclination is the angle between a
true vertical line starting at the center of the tire at
the road contact point and a line drawn through the
center of the upper ball joint (or strut) and the lower
ball joint (Fig. 5). S.A.I. is built into the vehicle and
is not an adjustable angle. If S.A.I. is not within
specifications, a bent or damaged suspension compo-
nent may be the cause.
INCLUDED ANGLE (I. A.)
Included angle is the sum of the S.A.I. angle plus
or minus the camber angle, depending on whether or
not the wheel has positive or negative camber (Fig.
5). If camber is positive, add the camber angle to the
S.A.I. angle. If camber is negative, subtract the cam-
ber angle from the S.A.I. angle. Included angle is not
adjustable, but can be used to diagnose a frame mis-
alignment or bent suspension component (spindle,
strut).
THRUST ANGLE
Thrust angle is the averaged direction the rear
wheels are pointing in relation to the vehicle’s center
line (Fig. 6). The presence of negative or positive
thrust angle causes the rear tires to track improperly
to the left or right of the front tires (dog tracking).
Fig. 3 Toe
1 - TOE-IN
2 - TOE-OUT
Fig. 4 Toe-Out On Turns
1 - TOE-OUT ON TURNS
Fig. 5 S.A.I. and I.A.
1 - S.A.I.
2 - CAMBER
3 - I.A.
2 - 50
WHEEL ALIGNMENT
PL/SRT-4
WHEEL ALIGNMENT (Continued)